Annealing process for magnetic material



1957 w. P. LANGWORTHY ANNEALING PROCESS FOR MAGNETIC MATERIAL 2Sheets-Sheet 1 Filed Oct. 7, 1953 BY W M ATTORNEYS Jan. 29, 1957 w. P.LANGWORTHY 2,779,699

\ ANNEALING PROCESS FOR MAGNETIC MATERIAL Filed Oct. 7, 1955 2Sheets-Sheet 2 FIG. 3.

INVENTOR ar/-14, LANG Jazz Twy ATTORNEYS ANNEALING PROCESS FOR MAGNETICMATERIAL William P. Langworthy, Philadelphia, Pa. Application October 7,1953, Serial No. 384,616

18 Ciaims. (Cl. 148-422) This invention relates to a coating andannealing process for magnetic materials and to a coated magneticmaterial produced by the foregoing process.

it is well known that magnet cores for use in alternating currentmachines, such as transformers, must be laminated in order to reduceeddy currents. Laminating the core is not effective unless thelaminations are insulated from each other. Moreover, in order to securebest results the laminations must be annealed in a high temperaturehydrogen atmosphere. While the effect of insulating the laminations andannealing the material may be determined experimentally in thelaboratory, it has been ditiicult to achieve low cost productionprocesses capable of attaining results such as those proved possible bylaboratory experiments. One difiiculty encountered in practice is thatduring the high temperature annealing step the laminations tend to stickand/or weld together. Another difficulty is attaining adequate exposureof the surfaces of the stacked laminations to the hydrogen annealingatmosphere or medium. Still another difiiculty involves obtaining inproduction at .a low cost a thin insulating coating onthe surface of thelaminations that will reduce eddy current. losses without seriouslyincreasing the thickness of the laminations. The principal object ofthis invention is to overcome the foregoing difficulties.

Another object of this invention is to provide an improved process forproducing coated laminations for electrical machines.

A still further object of the invention is .to provide an improvedcoated lamination for use in electrical machinery.

Other objects and advantages of t the invention will appear as thisdescription proceeds.

Others have discovered prior to my invention that a thick coating ofzirconium dioxide may be applied to a metal base by heating the metalbase to a temperature of several hundred degrees Fahrenheit and sprayingit with a water solution of ammonium zirconyl carbonate. 1 make no claimherein to that process but I claim the series of steps includingapplying that process to produce an extremely thin film on a metallicbase composed of material Whose magnetic properties are improved by ahigh temperature (about 1000 F. to 2350 .F.) hydrogen anneal, and thenexposing thecoated material to such an anneal. The results achieved bythis combination of steps are that the high temperature of the annealingstep drives oil the last traces of the water in the coating and thusimproves it. The coating step improves the annealing step by providing aporous film during the annealing step which separates the laminationssufliciently to allow the hydrogen atmosphere to contact the magneticmaterial and by separating the laminations to a sufficient extent thatthey do notstick together. Moreover, after the process is completed theresulting laminations have a very thin film that willinsulate them fromeach other afterthey are placed into use,

Hydrogen is the preferred atmosphere or-medium esr 2,779,699 PatentedJan. 29, 195.7

ice

pecially when the metal from which the laminations are stamped is one ofthe well known magnetic nickel alloys of iron, such as the Permalloys.One of these contains approximately 50% nickel, while the remainder isessentially iron. Another is composed of 79% nickel, 4% molybdenum andalmost pure iron to make up the remaining balance of almost 17%. Thesematerials may be annealed in a medium consisting of pure dry hydrogen,or if desired to make the process less expensive, the medium may becracked ammonia or any other desired mixture of hydrogen with nitrogen.Either of these media may be used in the annealing of the siliconcontaining magnetic alloys of iron, but to further decrease the cost ofthese materials they are often annealed in a so called burned-out-airmedium, which may contain variable amounts of nitrogen, carbon dioxide,carbon monoxide and perhaps hydrocarbons. Such anneals of thesilicon-iron alloys are usually done at a maximum ternperature in therange between about 1000 F. and i800 F., a value of 1450" F. being mostcommon.

The problems involved and the desirability of a coating for magneticlaminations are (llSC'dSSfidilIl U. S. Patent 2,410,220 to William P.Langworthy, dated October '29, 1946. The present invention describescertain improvements upon the basic teachings described and claimed inthat patent.

In the drawings:

Figure 1 illustrates one form of the process constituting my invention.

Figure 2 illustrates a coated lamination according to the invention.

Figure 3 illustrates a box of stacked laminations.

Figure 4 is a sectional View taken along line 4-4 of Figure 3.

Figure 5 is a photomicrograph of thecoated lamination following step Cof Figure l.

Figure 6 isa photomicrograph of the coated lamination after step E ofFigure 1.

Referring now .to Figure 1, step A involves stamping, a lamination ofsuitable magnetic material to proper shape and heat cleaning it at 800degrees, F. Other cleaning methods may of course be used. The materialis of a type Whose magnetic properties are improved by annealing it in ahigh temperature hydrogen atmosphere. One such material is Permalloywhich is a well known 'steel having about 50% nickel therein.

Step B involves heating the laminations singly or in groups to atemperature preferably between 300 and 600 degrees, Fahrenheit. Thelaminations are heated in a gas-fired or electric oven. An electricalinduction heater may also be used. if burning gas is used to heat thelaminations the products of combustion should not be allowed to contactthe laminations to avoid poisoning them. Step C involves passing theheated laminations one at a time through a mist or fog composed of anaqueous solution of ammonium zirconyl carbonate (hereinafter referred toas AZC). The mist of AZC solution may be produced, for example, bydirecting a spray toward the passing laminations. Preferably the AZCsolution is dilute but it maybe within the range of 0.l% to 12% byWeightof the equivalent contained zirconia (ZrOz}, 12% being thesaturation value. When the dilute mist strikes the hot laminations theAZC solution breaks down leaving a thin coating of a refractory metaloxide (ZrOz) on the surfaces of the laminations. The laminations remainat the aforesaid 300 to 600 degree temperature during the coatingoperation. The chamber or zone in which the mist or fog is created .mayencounter :an elevated temperature due to the heated laminationsipassingtherethrough.

.Step D involves stacking the .laminations after-they have cooled.Figure 3 illustrates how thezlaminations may be stacked in a traypreparatory for the annealing step. The tray has separators 11 and 12,and the laminations are stacked in rows as shown in Figure 4.Preparatory for the annealing step a number of trays of the type shownin Figure 4 may be placed on top of each other. These stacks of trays,so to speak, are placed in a heated hydrogen atmosphere for purposes ofannealing. Step E involves annealing the stacked laminations at a hightemperature in an annealing atmosphere or medium. In the case ofPermalloy, step E is carried out at 1800 to 2350 degrees Fahrenheit in ahydrogen atmosphere. In order for the annealing to have maximumbeneficial effect the hydrogen gas must permeate the pores of thelaminations. This is possible in the present case since the thin coatingseparates the laminations enough to allow hydrogen to enter between thelaminations. Moreover, the coating is rather spotty or discontinuousthus allowing the hydrogen gas to actually contact a very largepercentage of the total surface. The thickness of the coating and theextent of its coverage can be controlled somewhat by varying theconcentration of the solution in step C and also by varying the timeperiod that the laminations remain in the mist or fog of AZC solution.

The high temperature annealing step accomplishes the additional functionof driving off any remaining water of crystallization in the coating andthus improving it.

When the laminations have been annealed they are ready for use in atransformer or other electrical machine in the usual Way. Figure 2 is anillustration of the final product. The thin coating of zirconium dioxidecrystals insulates the laminations from each other. However, the coatingis so thin that it does not substantially increase the height of a stackof laminations. In technical language this means that the stackingfactor of the laminations is very favorable. For example it is possiblefor me to produce Permalloy laminations 0.006 inch thick with acontrolled coating thickness of from 1 to 1000 micro inches, asrequired.

There are other coating steps per se that may replace step C. Thesealternate coating steps per se are not my invention and are hereinafterclaimed only in combination with other steps. It may be stated as afundamental proposition that the coating step or material must notpoison the magnetic material or adversely affect its properties. Some ofthe substitutes for AZC may be defined by the following formula:

wherein X is a metal of group IV-A. In the event the metal is titanium,for example, the fog or mist would be a solution of ammonium titanylcarbonate. The corresponding analogs of aluminum (ammonium aluminumcarbonate) or magnesium (ammonium magnesium carbonate) may be used. Infact, the ammonium metal carbonate salts which may be used includeberyllium, thorium, magnesium, calcium, barium, strontium, aluminum,titanium, zirconium, hafnium, and cerium.

Another example of a suitable starting compound is a solution ofzirconium nitrate in anhydrous ethanol. Such a solution gives superiorresults, using temperatures of 400 to 1200" F.

Hence, step C involves a metal compound that breaks down when heated andreleases a compound (usually the oxide) of the metal. The startingmetallic compound should be in a solution or in essentiallysub-colloidal (less than 0.5 micron size) form in the solvent or vehiclewhich is removed by one or more of the heating steps of the wholeprocess. I

In all cases, the process is workable when the metal oxide content ofthe solution is between 0.1% and 10% by weight, and the temperature instep C is sufficient to cause the oxide to bond itself to the basemetal, usually several hundred degrees.

The zirconia coating is an improvement over the prior art since it doesnot poison or otherwise injure the magnetic materials.

Laminations produced by this process have an improved permeability ofabout 20% over laminations produced by present day prior art commercialprocesses. This is true over a wide range of flux density, for examplefrom 40 to 4000 gausses. In the prior art the permeability of stacks oflaminations varied substantially more from the overall average than istrue with the process herein claimed.

Moreover, the same size of tray will hold more laminations coated by myprocess than it will hold of prior art laminations since the coating isthinner. In fact it is possible in some cases to more than double thequantity of laminations that may be placed in an annealing furnace orcontainer of any given size. It has also been found that notwithstandingthe increased number of laminations placed in the tray the heat isconducted to the innermost parts of the tray quicker than in the priorart, this being due to the fact that coating is thinner than in theprior art. Hence, it is possible to carry out the process in a shortertime than has heretofore been customary.

Figures 5 and 6 are photomicrographs showing the thin discontinuouszirconia coating (which is white in color) on the magnetic base metal(which has dark color). Figure 5 was taken prior to step E and Figure 6after that step.

I claim to have invented:

1. The process of producing a part of an electrical machine, said parthaving magnetic properties, which includes, heating the part, passing itthrough a mist of a volatile substance containing an ammonium metalcarbonate salt that upon striking the heated part breaks down and leavesa thin discontinuous refractory metal oxide coating on the surface ofthe part, and then annealing the coated part at a temperature above thatused during the coating step, the annealing being carried out in thepresence of an annealing medium.

2. The process of producing coated laminations of material whosemagnetic properties are improved by a high temperature annealing in asuitable medium which includes stamping a lamination of said material,heating the lamination to a temperature in excess of 300 degreesFahrenheit, passing the heated lamination through a mist of a dilutesolution of ammonium zirconyl carbonate, stacking the laminations, andannealing the stacked laminatrons at a temperature higher than the oneto which the laminations were subjected during the hereinabove mentlonedheating step, the annealing being carried out in the presence of anannealing medium.

3. The process of producing coated laminations of Permalloy whichincludes stamping the Permalloy laminatlons, cleaning them, heating thelaminations to a temperature in the range of 300 to 600 degreesFahrenheit, exposing the laminations while thus heated to a mist of anaqueous solution of ammonium zirconyl carbonate, the solution havingbetween 0.1% to 12% by weight of zirconia content, stacking thelaminations, and annealing the stacked laminations in a hydrogen mediumat a temperature in the range of 1800 to 2350 degrees Fahrenheit.

4. The process defined in claim 3 in which the solution is so dilute andthe time of exposure of the laminations to the solution is so short thatthe coating formed on the laminations is discontinuous and of athickness less than 0.0005 inch.

5. The process of producing coated laminations which are composed ofmaterial whose magnetic properties are improved by a high temperatureannealing step which includes passing the laminations into a heatedzone, exposing the laminations while in said zone to a vehicle carryinga compound of zirconium which breaks down under the heat prevailing insaid zone and deposits a refractory oxide of zirconium on a surface ofthe laminations, and annealing the laminations at a still highertemperature.

6. The process defined in claim 5 in which the laminations are in theform of a stack during the annealing step.

7. The process of producing coated laminations of material whosemagnetic properties are improved by a high temperature annealing in asuitable medium which includes stamping a lamination of said material,heating the lamination to a temperature in excess of 300 degreesFahrenheit, passing the heated lamination through a mist of a dilutesolution of ammonium zirconyl carbonate while the lamination is at sucha high temperature that the ammonium zirconyl carbonate will. be brokendown leaving a coating of zirconium dioxide bonded to the lamination,stacking the laminations, and annealing the stacked laminations at atemperature higher than the one to which the laminations were subjectedduring the hereinabove mentioned heating step, the annealing beingcarried out in the presence of an annealing medium.

8. The process of producing coated laminations of Permalloy whichincludes stamping the Permalioy laminations, cleaning them, heating thelaminations to a ternperature in the range of 300 to 600 degreesFahrenheit, exposing the laminations while thus heated to a mist of anaqueous solution of ammonium zirconyl carbonate, the temperature of thelaminations while exposed to the ammonium zirconyl carbonate being sohigh that when contacted by the ammonium zirconyl carbonate the latterbreaks down and leaves a coating of zirconium dioxide bonded to thelaminations, the solution having between 0.l% to 12% by weight ofzirconia content, stacking the laminations, and annealing the stackedlaminations in a hydrogen medium at a temperature in the range of 1800to 2350 degrees Fahrenheit.

9. The process defined in claim 8 in which the solu tion is so diluteand the time of exposure of the laminations to the solution is so shortthat the coating formed on the laminations is discontinuous and of athickness less than 0.0005 inch.

10. The process of producing coated laminations which are composed ofmaterial whose magnetic properties are improved by a high temperatureannealing step which includes passing the laminations into a heatedZone, exposing the laminations while in said zone to a vehicle carryinga compound comprising an ammonium metal carbonate salt which breaks downunder the heat prevailing in said zone and deposit a refractory metaloxide on a surface of the laminations, and annealing the laminations ata still higher temperature, said compound being one characterized by thefact that it will not poison the magnetic material or adversely afiectits properties during the carrying out of said process.

11. The process defined in claim 10 in which the laminations are in theform of a stack during the annealing step.

12. The process of claim 10 in which the compound is ammonium zirconylcarbonate.

13. The process of claim 10 in which the compound is ammonium aluminumcarbonate.

14. The process of claim 10 in which the compound is ammonium magnesiumcarbonate.

15. The process of claim 10 in which the compound is ammonium calciumcarbonate.

16. The process of claim 10 in which the compound is ammonium titaniumcarbonate.

17. The process of producing coated laminations of material whosemagnetic properties are improved by a high temperature annealing in asuitable medium which includes forming a lamination of said material,heating the lamination, passing the lamination while in a heated statethrough a mist of a dilute solution or" ammonium zirconyl carbonate,said heating step raising the lamination to such a high temperature thatthe heat of the lamination will break down the ammonium Zirconylcarbonate mist which contacts it leaving a coating of zirconium dioxidebonded to the lamination, said mist being so dilute that the coatingwhich is formed will be discontinuous, and annealing the coatedlaminations at a temperature higher than the one to which thelaminations were subjected during the hereinabove mentioned heatingstep, the annealing being carried out in the presence of an annealingmedium.

18. The process defined in claim 17 which includes the additional stepof stacking the laminations before annealing them, the laminationsremaining in stacked form during the annealing step.

References Cited in the file of this patent UNITED STATES PATENTS1,842,162 Gifford Jan. 19, 1932 1,924,311 Frey Aug. 29, 1933 2,124,446Detwiler July 19, 1938 2,132,557 Bobrov Oct. 11, 1938 2,354,113 GouldJuly 18, 1944 2,410,200 Langworthy Oct. 29, 1946 2,475,601 Fink July 12,1949 2,515,788 Merrill July 18, 1950 2,540,623 Law Feb. 6, 1951

1. THE PROCESS OF PRODUCING A PART OF AN ELECTRICAL MACHINE, SAID PARTHAVING MAGNETIC PROPERTIES, WHICH INCLUDES, HEATING THE PART, PASSING ITTHROUGH A MIST OF A VOLATILE SUBSTANCE CONTAINING AN AMMONIUM METALCARBONATE SALT THAT UPON STRIKING THE HEATED PART BREAKS DOWN AND LEAVESA THIN DISCONTINUOUS REFRACTORY METAL OXIDE COATING ON THE SURFACE OFTHE PART, AND THEN ANNEALING THE COATED PART AT A TEMPERATURE ABOVE THATUSED DURING THE COATING STEP, THE ANNEALING CARRIED OUT IN THE PRESENCEOF AN ANNEALING MEDIUM.